When wind hits a microphone, a diaphragm included in the microphone vibrates largely, so that noise is included in an input signal. Here, if noise is included in the input signal, when speech recognition is performed or a hands-free phone call is made, the accuracy of the speech recognition and the quality of the phone call degrade. Therefore, in conventional speech recognition and a hands-free phone call, a conventional apparatus which suppresses irregular noise generated when wind hits the microphone is used.
FIG. 10 is a diagram illustrating an example of the conventional apparatus. As illustrated in FIG. 10, a conventional apparatus 10 is connected to microphones 10a and 10b. The microphones 10a and 10b are spaced apart from each other by a predetermined distance. The conventional apparatus 10 includes a correlation analyzer 11, a noise analyzer 12, and a noise reduction unit 13.
The microphone 10a is a microphone which converts collected sound into an input signal Lin(t) and outputs the input signal Lin(t) to the conventional apparatus 10. The microphone 10b is a microphone which converts collected sound into an input signal Rin(t) and outputs the input signal Rin(t) to the conventional apparatus 10. Here, t corresponds to a sampling number of the input signal.
The correlation analyzer 11 calculates a correlation value r(t) between the input signal Lin(t) and the input signal Rin(t) by using the formula (1). In the formula (1), the correlation analyzer 11 sequentially changes the value of i from 1 to n and calculates a correlation value r(t). For example, the value of n is 128. The correlation analyzer 11 outputs the correlation value r(t) to the noise analyzer 12.r(t)=ΣLin(t−i)Rin(t−i)/((ΣLin(t−i)2)1/2(ΣRin(t−i)2)1/2)  (1)
When the value of the correlation value r(t) is small, the noise analyzer 12 determines that there is noise of wind and outputs control information to turn down volume to the noise reduction unit 13.
The noise reduction unit 13 adjusts the volumes of the input signals Lin(t) and Rin(t) and outputs the input signals Lin(t) and Rin(t) to an external apparatus. For example, when the noise reduction unit 13 receives the control information to turn down volume, the noise reduction unit 13 turns down the volumes of the input signals Lin(t) and Rin(t) and outputs the input signals Lin(t) and Rin(t) to the external apparatus.
Patent Document 1: Japanese Laid-open Patent Publication No. 2004-289762
Patent Document 2: Japanese Laid-open Patent Publication No. 2009-005133
However, in the conventional technique described above, there is a problem that noise included in a target input signal such as voice is not sufficiently suppressed.
For example, in the conventional technique, when wind blowing against the microphone is strong, the noise of the input signal can be suppressed. However, when wind blowing against the microphone is weak, the difference of correlation coefficient between a section including voice and a section including wind hitting noise is small, so that the noise is not accurately suppressed.